From 1930 to 1939 fire ants spread inland about 60 miles from their point of introduction in mobile, alabama. what was the cause of their spread over this distance? from 1930 to 1939 fire ants spread inland about 60 miles from their point of introduction in mobile, alabama. what was the cause of their spread over this distance? a natural spread airplanes being transported along with soil being transported along with plants dispersion via ship ballast